1. Field of the Invention
This invention resides in the field of preparative chromatography columns.
2. Description of the Prior Art
Preparative chromatography is a separation technique used to extract individual chemical species in quantities sufficient for commercial use from mixtures of species. Preparative chromatography thus differs from analytical chromatography whose purpose is to detect the presence or concentration of particular components in the mixture or to determine the composition of the mixture as a whole. Preparative chromatography is commonly performed by passing a relatively large quantity of a liquid source mixture through a column packed with a solid resin. Separation of the different species in the mixture and extraction of the species of interest can occur by any of a wide variety of interactions between the source mixture solution, referred to as the mobile phase, and the resin, referred to as the stationary phase. Examples of these interactions are ion-exchange chromatography, affinity chromatography, and liquid-liquid or partition chromatography.
In an axial-flow preparative chromatography column, the axial length of the column must be limited to avoid an excessive pressure drop through the column, since a high pressure drop requires a high pump pressure to force the mobile phase through the column, high power to drive the pump, or both. To extract the separated species in a commercially useful quantity, therefore, a column of relatively large diameter is needed. The typical preparative chromatography column is thus at least several centimeters in diameter, and in some cases, columns with diameters of a meter or more are used. Columns of large diameters present certain challenges, however, notably the difficulty in distributing the flow of mobile phase across the width of the column, as one needs to do to achieve efficient separation and a high resolving power. Flow distributors are typically used at both ends of the column to overcome this problem. In some cases as well, particularly in columns that are arranged vertically with downward flow, the solid phase is packed in the column in a manner that eliminates or minimizes void spaces at the inlet side of the packing. Uniform packing can be achieved by applying pressure to the resin particles, but pressure can also cause fracture or pulverization of portions of the packing material, particularly if the material is incompressible such as ceramic hydroxyapatite or fragile such as controlled-pore glass. The pressure can be applied by use of a sliding piston, also referred to as an adaptor, that is positioned above the resin and is lowered until it contacts the resin. The piston that is typically used also contains flow distribution channels to help distribute the mobile phase across the column width. To avoid damage to the resin particles, the movement of the piston must be closely controlled. Caution is also needed for compressible resins, particularly those resins designed to be compressed by a set percentage relative to their uncompressed state. For these resins, the total amount of resin in the column prior to compression must be known.